In my prior U.S. Pat. No. 7,146,672 I disclosed a tunable load sharing double arch bridge where the terminal ends of the arches are anchored to the ends of the lower chords of a truss girder deck. A tension member spans the lower chords of the truss girder deck and a plurality of spaced apart adjustable hanger rods interconnect each arch and the respective lower chord of the truss girder deck. Dead and live loads on the bridge structure are shared between the truss girder and the arches as a function of the respective tension adjustment in the tension member/s that span the lower chords and the tension forces in the hanger rods. Tension that is created in the member that spans the lower chord creates compression in the lower chord of the truss girder. Accordingly, the compression reduces the dead load tension forces in that lower chord. Live loads are shifted to the arches by adjusting the tension forces within the hanger rods that depend from the arches. By judicious adjustment of the respective tensions in the spanning member/s and the hanger rods the sharing of live and dead loads can be apportioned between the truss girder and the arches. Such allocation of forces permits the use of lighter weight structural materials and easier and less expensive construction costs.
The primary benefits of the invention disclosed in the '672 patent are achieved in the first instance by the tension member that spans the lower chord of the truss girder. The object of the present invention is to eliminate or at least significantly reduce the size of the spanning tension member while still achieving the same result, that is, reducing or eliminating the tension in the lower chord of the truss girder. When tension is reduced or eliminated in the lower chord the compression forces in the upper chord are also equalized.
A second objective of the present invention is to reduce the size and cost of materials necessary to construct a bridge by judiciously allocating the dead and live loads between various structural members of the bridge.
A further object of the invention is to create a bridge in which there is no critical structural member, thus eliminating the possibility of catastrophic failure of the structure upon the failure of one member.
A still further object of the invention is to provide a combination arch and beam where the tension and compression in the respective bottom and top flanges of the beam are equalized by the arch and its novel attachment to the beam.
Other and still further objects, features and advantages of the invention will become apparent upon a reading of the following detailed description of a preferred form of the invention taken in conjunction with the accompanying drawings.